Apparatus and method for tripping a safety system for the protection of an occupant of a vehicle

ABSTRACT

An apparatus and method for actuating a safety system for protecting an occupant of a motor vehicle measures the acceleration of the vehicle with a first sensor along a first axis oriented substantially parallel to the forward direction of motion of the vehicle. The acceleration of the vehicle is also measured with a second sensor along a second axis oriented at an angle relative to the first axis. The acceleration signal generated by the first sensor is evaluated by an analog processor and the acceleration signal generated by the second sensor is evaluated by a digital processor. The safety system is then actuated based upon both the analog and digital evaluations.

This application is a continuation of application Ser. No. 08/166,169,filed Dec. 10, 1993, now U.S. Pat. No. 5,449,198 which in turn is acontinuation of application Ser. No. 07/623,945, filed Feb. 11, 1991which is a continuation of PCT/EP88/00508 filed Jun. 9, 1988.

STATE OF THE ART

The present invention relates to an apparatus and method for trippingsafety systems for the protection of an occupant of a vehicle, in whichthe acceleration of the vehicle is measured along a first axis orientedsubstantially parallel to the forward direction of the vehicle and ismeasured along a second axis oriented at an angle relative to the firstaxis.

Systems are known which have one or more acceleration sensors whichmeasure the acceleration of the vehicle both in the direction of traveland also at right angles thereto. After suitable processing, the signalsserve to trip corresponding safety systems, such as inflatable airbags,the tightening of seat belts, central door locking and flashing warningsystems.

The signals from the sensors may be processed by analog systems or bydigital systems. Analog processing has the advantage of rapid andreasonably accurate processing of the signals, and thus has theadvantage of speed over digital systems (which require computerprocessing) in the event of a very violent impact.

On the other hand, computer processing makes it possible to utilize moreexpensive and more accurate evaluation methods, but has thedisadvantages of increased cost and increased processing time. Thelatter disadvantage must particularly be taken into consideration sinceit is necessary to detect an acceleration for which tripping is requiredas soon as possible.

It is an object of the present invention to provide an apparatus andmethod for tripping the safety system, which utilizes as far as possiblethe advantages of both analog and digital processing.

ADVANTAGES OF THE INVENTION

The above object is achieved by the device and method according to thepresent invention, which has the advantage of utilizing both the rapidreaction time of analogue processing and the accuracy of digitalprocessing.

DRAWINGS

By way of example only, specific embodiments of the present inventionwill now be described, with reference to the accompanying drawings, inwhich:

FIG. 1 is a diagrammatic representation of a first embodiment of adevice for tripping safety systems, in accordance with the presentinvention; and

FIG. 2 is a diagrammatic representation of a second embodiment of adevice for tripping safety systems, in accordance with the presentinvention.

DESCRIPTION OF EXEMPLARY EXAMPLES

Referring firstly to FIG. 1, the device comprises longitudinalacceleration sensor 10, for detecting the acceleration of the vehicle ina direction parallel to the forward direction of motion of the vehicle,and a transverse acceleration sensor 12, for detecting the accelerationof the vehicle in an axis substantially perpendicular to theaforementioned axis (hereinafter referred to as the transversedirection). The analog output of the longitudinal acceleration sensor 10is fed to an analog evaluation circuit 14 which evaluates the mainacceleration signal (in the direction of forward travel of the vehicle)by known methods. If the evaluation circuit 14 determines that theacceleration in the longitudinal direction is greater than apredetermined value, then an actuating signal is fed to an output stage16 which in turn trips the safety system (for example an inflatableairbag).

In this way, when the longitudinal acceleration above a certainthreshold value, the safety device is actuated.

The output of each of the sensors 10, 12 is fed to a respective low-passfilter 18, 20. The limiting frequency of the low-pass filters is chosensuch that it does not serve solely for the evaluation of theacceleration signal. Only the higher frequencies which contain moreaccurate information (which is not ascertainable from the analog signal)are integrated. Pre-processing is thus achieved in a desired manner,with the resultant advantage that the signal scan frequency can bereduced, and more time-consuming computing algorithms can be used forthe subsequent evaluation of the two signals.

The output from both of the low-pass filters 18, 20 is fed to an analogto digital converter (ADC) 22, wherein the signals are converted todigital signals. The now digital signals are then fed into a digitalcomputer 24, which evaluates the acceleration signals from the sensors10, 12 digitally.

The process evaluation signal is then fed to the analog evaluationcircuit 14 via a digital to analog converter (DAC) (not illustrated).Depending upon the evaluations made by the computer 24, the analogevaluation circuit 14 may determine that a signal ought to be sent tothe output stage 16, even if the value of the longitudinal accelerationis not sufficient by itself for the safety device to be triggered. Forexample, the relative values of the longitudinal and transverseacceleration of the vehicle, as evaluated digitally in the computer 24may be such that the overall acceleration is sufficiently large towarrant tripping of the safety device. This may occur, for example, inan oblique impact, where the longitudinal acceleration itself may not besufficient to trip the safety device, but the magnitude of theacceleration total is such that actuation of the safety device isdesirable.

The second embodiment of the present invention illustrated in FIG. 2.Longitudinal and transverse acceleration sensors 10, 12 are provided, asin the first embodiment.

The output from the longitudinal acceleration sensor 10 is fed into ananalog evaluation circuit 30. The output of the analog evaluationcircuit 30 is fed firstly to a tripping threshold switch dV, andsecondly via a low-pass filter and ADC (not illustrated) to a firstcomputer 32 of the digital processing system.

The output of the longitudinal acceleration sensor 10 is also fed via alow-pass filter (not illustrated) to an ADC 34, and thence into the first computer 32. The outputs of the longitudinal and the transversesensors 10, 12, respectively, after passing through respective low-passfilters (not illustrated) are fed into a second ADC 36, and thence intoa second computer 38.

The digital circuitry thus calculates the longitudinal accelerationdigitally in the computer 32. The longitudinal and trans verseaccelerations are also compared in the second computer 38, and thisinformation is fed into the first computer 32. The output of thecomputer 32 is fed to the tripping threshold switch dV, which actuatesan output stage 40 to trip the vehicle safety device if a suitablesignal is fed therein.

Triggering of the safety system can occur in one of three general ways.Firstly, either the signal of the analog channel or the longitudinalsignal of the digital channel can determine that a thresholdacceleration has been reached, and a suitable signal is sent to thethreshold switch dV which operates to actuate the safety device. In thissituation, it will normally be the analog channel which produces itssignal first of all, due to its faster processing. However, inborderline cases the analog channel may not be sufficiently accurate todetermine that a threshold acceleration has been reached, whereas themore accurate digital channel is capable of doing so. Thus, in certainborderline cases it may be the digital channel which triggers theactuation of the safety device, albeit slightly later than would haveoccurred for the analog channel.

Secondly, the digit al processor may reach a tripping threshold by itself, the analog channel signal not reaching the longitudinalacceleration threshold. This may occur, for exam pie, in an obliqueimpact, where a significant acceleration is experienced by the vehiclein the transverse direction. In this case neither the analog processingcircuitry 30 nor the first computer 32 would detect a longitudinalacceleration threshold, but the second computer 38, on comparing thelongitudinal and transverse accelerations, would inform the computer 32that actuation of the safety device is warranted and the computer 32would output a suitable signal to the threshold switch dV accordingly.In this second case, the threshold switch dV is preferably arranged toprovide a tripping signal from the digital circuitry, only if a signalfrom the analog channel is also received. Such a signal from the analogchannel indicates that there is a component of the vehicle accelerationin the longitudinal direction, and this provision helps to ensureagainst the possibility of incorrect calculation by one of the computers32, 34, and subsequent incorrect tripping. A predetermined value of thelongitudinal acceleration calculated by the analog circuit is preferablyspecified in this case.

The third case is that the tripping threshold switch dV is actuated onlyby the analog channel, but the connection between the computer 32 of thedigital circuitry and the analog evaluation circuitry 30 allows thedigitally-calculated signals to influence the evaluation carried out bythe analog evaluation circuit 30. This is why the connection between thecomputer 32 and the tripping threshold switch dV has been dotted, sincein this case there would be no direct connection from the computer 32(or, indeed, any of the digital circuitry) and the tripping thresholdswitch dV. In this case, the tripping threshold switch dV can beactuated only by the analog evaluation circuitry 30, but the analogcircuit 30 can, in turn, be influenced by the digital circuits. Forexample, the analog circuit 30 may calculate that the longitudinalacceleration is not of sufficient value to initiate tripping of thesafety device. However, the digital circuitry may calculate that theoverall acceleration (or, for example, the relative longitudinal andtransverse accelerations) is of sufficient value to warrant actuation ofthe safety device. In this case, the information from the digitalcircuitry would be fed into the analog circuit 30 and the analogcircuit, depending on the information fed into it from the digitalcircuitry, would send a suitable actuation signal to the trippingthreshold switch dV.

The present invention is suitable in all types of impact as follows.

1. Rapid Frontal Impact

The characteristic of such an impact is a very rapid and high increasein the tripping signal. Such impact requires rapid evaluation of thelongitudinal acceleration. This can be achieved either by taking theanalog signal directly, or by processing the acceleration in thecomputer 32 and merely having the analog signal as a "confirmation" orback-up signal. As stated previously, the latter situation might be ofbenefit if the value of the acceleration was a borderline case.

2. Slow Frontal Impact

This type of impact has a rapid but small increase the tripping signal.This requires rapid and accurate evaluation of the longitudinalacceleration. This is preferably achieved by processing in the computer32, provided that the additional analog tripping circuit 30 reaches thelow threshold described previously. A further check on the plausibilityof the calculated signal may be made by the computer 38, whichcalculates the values of the longitudinal and transverse accelerationsand feeds this information into the computer 32.

3. Oblique Impact (e.g. 30°)

This type of impact has a slow and variable increase in the longitudinaltripping threshold signal, less in the initial phase than in the case ofa slow frontal impact. Relatively slow but accurate evaluation of theacceleration is required. This is achieved by computer 32 (provided theadditional analogue tripping circuit reaches the low threshold) toevaluate the longitudinal signal, and computer 38 which is used tocalculate the transverse signal, and feed this information to computer32.

4. Rear Impact

This type of impact has an increase in the tripping signal in a negativedirection, and an increase in a positive direction at the end of thecrash (high-pass behavior). No tripping is desired in such an impact,and this is achieved by the computer 32 being able to integrate in bothdirections.

5. Side Impact

Such an impact has the characteristic of a large transverse signal. Notripping of the safety system is desirable or required in such animpact. This is achieved by computer 38 which blocks computer 32, sincethe ratio of the longitudinal and transverse accelerations is not withinthe actuation threshold. Even if computer 38 gave a false signal, therewould still be the emergency longitudinal back-up provided by the analogcircuit 30.

The present invention is particularly suitable for safety devices suchas inflatable airbags and the actuation (i.e. locking) of seatbelts.However, it may also be used to actuate flashing warning light systems,unlock the doors centrally, or to actuate other safety features.

I claim:
 1. A system for activating an occupant protection device of avehicle, comprising:an acceleration sensor for detecting an accelerationof the vehicle and for generating an acceleration signal indicative ofthe detected acceleration; a digital determination device for receivingthe acceleration signal, for determining, in a digital manner, anoccurrence of a collision of the vehicle in response to the accelerationsignal, and for generating a first trigger signal based upon the digitaldetermination; an analog determination device for receiving theacceleration signal, for determining, in an analog manner, an occurrenceof a collision of the vehicle in response to the acceleration signal,and for generating a second trigger signal based upon the analogdetermination; and a control device for receiving the first and secondtrigger signals and for controlling activation of the occupantprotection device as a function of at least one of the first and secondtrigger signals.
 2. The system according to claim 1, wherein the controldevice controls activation of the occupant protection device as afunction of both the first and second trigger signals.
 3. A method ofactivating an occupant protection device of a vehicle, comprising thesteps of:detecting an acceleration of the vehicle; generating anacceleration signal indicative of the detected acceleration;determining, in a digital manner, an occurrence of a collision of thevehicle in response to the acceleration signal; generating a firsttrigger signal based upon the digital determination; determining, in ananalog manner, an occurrence of a collision of the vehicle in responseto the acceleration signal; generating a second trigger signal basedupon the analog determination; and controlling activation of theoccupant protection device as a function of at least one of the firstand second trigger signals.
 4. The method according to claim 3, whereinactivation of the occupant protection device is controlled as a functionof both the first and second trigger signals.
 5. The method according toclaim 3, wherein the second trigger signal is generated as a function ofthe first trigger signal.
 6. A system for actuating a safety device forthe protection of an occupant of a vehicle, comprising:a first sensoradapted to generate a first signal indicative of an acceleration of thevehicle along a first axis; a second sensor adapted to generate a secondsignal indicative of an acceleration of the vehicle along a second axisoriented at an angle relative to the first axis; a controller includinga digital collision determination device and an analog collisiondetermination device, each of the digital and analog collisiondetermination devices being coupled to at least one of the first sensorand the second sensor, the controller being adapted to control actuationof the safety device as a function of the first and second signals, thesafety device being actuated if the value of the first signal exceeds anactuation threshold value, regardless of the value of the second signal.7. The system according to claim 6, wherein the second axis is orientedat a right angle relative to the first axis.
 8. The system according toclaim 6, wherein the first axis is oriented in a direction of forwardmotion of the vehicle.
 9. A system for actuating at least one safetydevice for the protection of an occupant of a vehicle, comprising:afirst sensor for sensing an acceleration of the vehicle along a firstaxis and for generating a first acceleration signal based thereon; asecond sensor for sensing an acceleration of the vehicle along a secondaxis oriented at an angle relative to the first axis and for generatinga second acceleration signal based thereon; an analog collisiondetermination device coupled to the first sensor for receiving the firstacceleration signal and for determining, in an analog manner, anoccurrence of a collision of the vehicle and the value of a firsttrigger signal indicative of whether the safety device should beactuated in response to the first acceleration signal; and a digitalcollision determination device coupled to the second sensor forreceiving the second acceleration signal and for determining, in adigital manner, an occurrence of a collision of the vehicle and thevalue of a second trigger signal indicative of whether the safety deviceshould be actuated in response to the second acceleration signal;wherein the safety device is actuated as a function of the first andsecond trigger signals.
 10. The system according to claim 9, wherein thefirst axis is oriented in a direction of forward motion of the vehicle.11. The system according to claim 10, wherein the second axis isoriented at a right angle relative to the first axis.
 12. The systemaccording to claim 9, wherein the safety device is actuated when thefirst acceleration signal exceeds a threshold value.
 13. The systemaccording to claim 9, wherein the digital collision determination deviceis coupled to the analog collision determination device.
 14. The systemaccording to claim 9, further comprising at least one low-pass filter,the low-pass filter feeding the first and second acceleration signals tothe digital collision determination device.
 15. A system for actuatingat least one safety device for the protection of an occupant of avehicle, comprising:a first sensor for sensing an acceleration of thevehicle along a first axis and for generating a first accelerationsignal based thereon; a second sensor for sensing an acceleration of thevehicle along a second axis oriented at an angle relative to the firstaxis and for generating a second acceleration signal based thereon; ananalog determination device coupled to the first sensor for receivingthe first acceleration signal and for determining, in an analog manner,the value of a first trigger signal indicative of whether the safetydevice should be actuated in response to the first acceleration signal;and a digital determination device coupled to the second sensor forreceiving the second acceleration signal and for determining, in adigital manner, the value of a second trigger signal indicative ofwhether the safety device should be actuated in response to the secondacceleration signal; wherein the safety device is actuated as a functionof the first and second trigger signals; wherein the safety device isactuated when the digital determination device determines that thesafety device should be actuated based upon the second accelerationsignal.
 16. A system for actuating at least one safety device for theprotection of an occupant of a vehicle, comprising:a first sensor forsensing an acceleration of the vehicle along a first axis and forgenerating a first acceleration signal based thereon; a second sensorfor sensing an acceleration of the vehicle along a second axis orientedat an angle relative to the first axis and for generating a secondacceleration signal based thereon; an analog determination devicecoupled to the first sensor for receiving the first acceleration signaland for determining, in an analog manner, the value of a first triggersignal indicative of whether the safety device should be actuated inresponse to the first acceleration signal; and a digital determinationdevice coupled to the second sensor for receiving the secondacceleration signal and for determining, in a digital manner, the valueof a second trigger signal indicative of whether the safety deviceshould be actuated in response to the second acceleration signal;wherein the safety device is actuated as a function of the first andsecond trigger signals; wherein the safety device is actuated when theanalog determination device determines that the safety device should beactuated based upon the first acceleration signal.
 17. A method ofactuating at least one safety device for the protection of an occupantof a vehicle, comprising the steps of:sensing an acceleration of thevehicle along a first axis and generating a first acceleration signalbased thereon; sensing an acceleration of the vehicle along a secondaxis oriented at an angle relative to the first axis and generating asecond acceleration signal based thereon; determining, in an analogmanner, an occurrence of a collision of the vehicle and the value of afirst trigger signal indicative of whether the safety device should beactuated in response to the first acceleration signal; determining, in adigital manner, an occurrence of a collision of the vehicle and thevalue of a second trigger signal indicative of whether the safety deviceshould be actuated in response to the second acceleration signal; andactuating the safety device as a function of the first and secondtrigger signals.
 18. The method according to claim 17, wherein the firstaxis is oriented substantially parallel to the forward direction ofmotion of the vehicle.
 19. The method according to claim 17, wherein thevalue of the first trigger signal is determined as a function of thevalue of the second trigger signal.